| dc.description.abstract | This research presents the methodology and the results of numerical studies on turbulent flows in a piping system that resembles the geometry of the Fission Product Venting System (FPVS) in High-Temperature Gas-Cooled Fast Reactors (HTGR). The fission product includes graphite particulates carried by coolant as flows through the core and fission gases like Krypton, Xenon, Cesium, and Iodine produced from thermonuclear reaction. Knowing the location of mixing and the magnitude of various gaseous components is necessary to manage and mitigate the adverse effects of fission products on power generation. In this work, scaling analysis was used to identify the geometry, surrogate gases, and surrogate particles. The turbulent flow fields in the piping system were simulated using the openFOAM v7 and Large Eddy Simulation (LES). The grid independence was established using the Grid Convergence Index (GCI) concept. In addition, numerical simulations were validated against the experimental data and the Direct Numerical Simulation (DNS) data reported in the literature. The quantities of interest, such as reattachment length and critical point of flows through axisymmetric expansion and the Absolute Mixing Index (AMI) through a piping system with 90 deg bend, were calculated. The reattachment length represents the length of the recirculation region, and the critical points (Cr1 and Cr2) represent the cross-over points from laminar to transition region, and the transition region to turbulent flow. A series of parametric runs were made by varying flow Reynolds number (Re), turbulence intensity (TI) at the inlet, and surrogate gas concentration at the injection point. Using the parametric runs design, correlation expressions for reattachment length and the critical point were developed. The gradient of log10AMI represents the mixing rate, and the highest value is observed downstream of the pipe’s expansion. The AMI is the standard deviation of the concentration of the surrogate gas Argon in the piping system. The Proper Orthogonal Decomposition (POD) technique was used to study the coherent turbulent structure downstream of a sudden expansion. Finally, simulation of the surrogate solid particles was carried out using the Lagrangian approach. The deposition velocity particles in a square horizontal channel were estimated using a discrete random walk model. | |
